Circuit interrupter



Patented June 10, 1952 UNITED STATES PATENT OFFICE Freese,

East McKeesport, Pa.,

assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 10, 1944, Serial No. 562,805

14 Claims. (Cl. 200-116) This invention relates in general to electric circuit interrupters, and more especially to circuit breakers.

In small circuit breakers of the type having a pivoted contact arm, difficulty has been encountered in certain applications, due in part to space limitations, in obtaining uniform contact pressure, especially after the parts have become worn in use.

One object of this invention, therefore, is to provide in a circuit breaker, novel means for obtaining uniform contact pressure regardless of wear encountered in use.

Another object of this invention is to provide novel means for obtaining uniform contact pressure for circuit breaker contacts which also contributes to the efficiency of operation of the contact actuating mechanisms.

Another object of this invention is to provide a novel contact structure for circuit breakers which provides a wiping action of the contacts during their operation.

Another object of this invention is to provide a novel circuit breaker structure which is effioient in operation and economical to manufacture.

These and other objects of this invention will become more apparent upon consideration of the following detailed description of a preferred embodiment thereof, when taken in connection with the attached drawings, in which:

Figure 1 is a longitudinal section view of a circuit breaker constructed in accordance With this invention with one supporting plate for the breaker mechanism removed to show the mechanism in elevation, and with the arc confining structure shown in section to better illustrate the construction thereof;

Fig. 2 is a transverse section view of the breaker shown in Fig. 1 taken substantially on the line II-II thereof;

Fig. 3 is also a transverse section view of the breaker shown in Fig. 1, but taken substantially on the line III-III thereof;

Fig. 4 is a View similar to Fig. l of a part of the breaker mechanism, illustrating a slightly modified form of movable contact construction;

Fig. 5 is a view similar to Fig. 4, but illustrating another modified contact construction;

Fig. 6 is a view similar to Figs. 4 and 5, but illustrating a further modified contact construc tion;

Fig. 7 is a view like Figs. 1 to 6, of still another modified contact construction.

The circuit breaker is illustrated on the drawings as being confined in a casing of insulating material, preferably of a molded insulating material or the like. The casing comprises two half portions including a base portion 2, and a cover portion 4, secured together as by bolts passing through aligned openings provided in each casing portion. In the particular form of casing illustrated, bolts 6 may be provided onl in diagonal ly opposite corners of the casing, with the aligned bores 8 provided in the other pair of diagonally opposite corners of the casing being left for the reception of mounting bolts or the like.

The circuit breaker mechanism is for the most part supported between a pair of spaced sup porting plates H) of like configuration, within the insulating casing. Supporting plates is are disposed adjacent the side walls of the casing, and each plate is provided with integral extensions ll adapted to project through openings provided in the bottom Wall of the casing, and to be riveted over on the outside of the casing as at 15, to secure the supporting plates in operative position in the casing. Supporting plates iii are also secured together by connecting rivets l2 and [3, to prevent relative movement of the plates. Rivets l2 and it are located with respect to the plates in the particular positions shown in Fig. l, for a purpose to be described.

A movable contact bar 22 is adapted to be supported between supporting plates iii, and for this purpose is provided with a slot 28 for receiving a pivot pin it having reduced ends adapted to be received in supporting plates it. Contact bar 22 is provided with a contact 26 at the outer end thereof, which is preferably of some good are resistant conducting material, such as a silver alloy. Contact 24 on the movable contact bar is adapted to engage a fixed contact of similar material, secured by means of a rivet 28 to the bottom wall of the breaker casing. Rivet 28 also supports on the exterior of the casing a terminal strap (iii, having a terminal screw 32, by means of which a circuit conductor may be electrically connected with the breaker. Contact bar 22 is biased by a leaf spring 34 engaging a projection 38 on the inner end thereof, to urge contact bar 22 in a direction to cause the bottom of slot 20 to engage pivot pin it. illustrated in the drawings, biasing spring is has angularly directed ends adapted to be received in spaced depressions 36 provided in the bottom wall of the casing. Preferably, extension 38 on the contact bar which engages leaf spring 34 is rounded, so that these parts engage on substantially a line of contact, and since in 3 the closed circuit position of the device this point of contact is directly radially below pivot pin it, spring 34 has no tendency to cause rotation of contact bar 22 about rivet HE.

A carrier bar 40 is also supported between supporting plates H], by means of a pivot pin l4, having reduced ends received in openings provided in supporting plates l0. Normally carrier bar 40 is maintained against clockwise movement about pivot pin l4, by engagement of a nose 42 thereof beneath latch pin 44. A trip member or latch 46, which is pivotally mounted between supporting plates on a pivot pin l8, carries latch pin 44, and is adapted to be actuated and controlled in a manner to be hereinafter described. The actuating mechanism for movable contact bar 22 is connected between carrier 43 and contact bar 22, and comprises a pair of toggle links 4'! pivotally mounted on carrier bar 40 as by a pivot pin 48. A second pair of toggle links 52 is pivotally mounted on contact bar 22 as by a pivot pin 54, and these toggle links are pivotally connected with toggle links 4'], by a knee pivot pin 59.

In order to actuate the toggle mechanism comprising links 4'! and 52, a pair of actuating levers 55 have their inner ends pivotally received in the rounded inner ends of substantially V-shaped notches 58, provided in the upper side of each supporting plate 10. Actuating levers 56 are rigidly connected together by a connecting rivet 62, and the inner ends of these levers are prevented from moving laterally out or" notches 58 by means of plates 69 which are secured to supporting plates ii] at the inner ends of notches 58. A pair of overcenter tension springs 64 are connected between knee pivot pin 53 of the toggle levers and connecting rivet 52 of the actuating levers, for the purpose of actuating the toggle levers and consequently contact bar 22 with a snap action, upon pivotal movement of actuating levers 53.

In the operation of the parts of the circuit breaker thus far described, it will be observed that in the closed circuit position shown in Fig. l, toggle levers 4i and 52 are held at an extended position slightly beyond the dead-center position, where overcenter spring 64 holds knee pivot pin 58 of the toggle in engagement with the adjacent edge of angular portion 65 of carrier 4! Now assuming it is desired to open the breaker contacts, actuating levers 56 are pivotally moved to the left, or in a counterclockwise direction, to carry the upper ends of overcenter springs 84 past toggle pivot 42. As soon as this occurs, the spring is effective to cause collapse of the toggle levers to the left, and thereby separate contact 24 from fixed contact 25. It will be noted that in the closed circuit position, the toggle is effective to stress leaf spring 34 so that pivot pin I6 is located at an intermediate position in slot 28. Leaf spring 34 thus serves to determine the pressure with which contact 24 engages contact 26, because this spring in the closed circuit position tends to rotate contact 24 into engagement with contact 26 about pivot pin 54. Accordingly, when the circuit is opened by collapse of the toggle, as described above, biasing spring 34 moves the adjacent end of contact bar 22 relative to pivot pin I6, until the bottom of slot engages the pivot pin, and thereafter movement of the contact bar 22 is purely pivotal relative to pivot pin it. In closing the circuit, the reverse operation takes place, that is, actuating levers 56 are pivotally moved back to the position shown in Fig. 1 to straighten the toggle, thus causing pivotal movement of contact bar 22 in clockwise direction relative to pivot pin [6 until contact 24 engages fixed contact 26, whereupon this pivotal movement ceases, and the remaining movement of toggle levers 41 and 52 to the position shown in Fig. 1 results in stressing biasing spring 34 by substantiaily pivotal movement of the contact bar about the point of engagement thereof with fixed contact 25, in a counterclockwise direction.

By the provision of contact biasing spring 34 at the pivotal mounting of movable contact bar 22, a substantially constant contact pressure is provided, while at the same time allowance is made for any variation in the parts as manufactured, as well as for wearing of the contacts proper, by virtue of the fact that biasing spring 34 is adapted to be stressed a substantial amount. Thus, any dimensional variation in the parts will merely result in more or less stress imposed on spring 34 at the close circuit position, and, of course, contact wear is compensated for in the same way by spring 34.

A bimetal strip 66 is provided within the breaker casing for the purpose of controlling latch lever 46, and this bimetal strip is constructed in a manner well known in the art, of a pair of laminations of materials having, respectively, high and low thermal coefficients of expansion, with the strip arranged so that the high coefiicient of expansion lamination is adjacent latch lever 46, so that when the bimetal strip is heated it will deflect to the left at the upper end, as viewed in Fig. 1. Bimetal strip 66 has the lower end thereof bent at an angle to be secured to the bottom wall of the breaker casing by a rivet 13, which also acts to secure a terminal strip 74 at the outside of the casing. Terminal strip '54 is provided with a terminal screw 16 similar to terminal screw 32, for making electrical connection with another circuit conductor. Bimetal strip 65 has at the upper end thereof, a threaded opening for receiving a screw 63 which has an enlarged head 10, adapted to engage behind projection 72 on latch lever 46.

The electric circuit through the circuit breaker may now be traced from terminal strip 14 through rivet l3, bimetal strip [55 and a flexible shunt l8 connecting a midpoint of bimetal strip 66 to contact bar 22, to contact 24 and contact 26 when the parts are in the closed circuit position, thence by rivet 28 to terminal strip 30. Although bimetal strip 66 is thus at least partly electrically connected in series in the circuit through the breaker so as to be heated directly by currents in excess of a predetermined value to cause deflection thereof, it is obvious that it may not be in the electric circuit at all, but may be heated by a separate heater connected in series in the circuit, in a manner well known in the art. It will be apparent that when bimetal strip 68 is heated and the upper end thereof deflects to the left, as viewed in Fig. i, it will move latch lever 46 in the same direction, or counterclockwise about its pivot l8, until latch pin 44 escapes from nose 42 of carrier 40, to thus permit overcenter springs 64 to bodily raise the toggle levers while rotating carrier 40 in a clockwise direction about its pivot l4, to thus move contact bar 22 to open circuit position, substantially in the manner previously described. It will be noted that latch lever 46 is biased in a clockwise direction as viewed in Fig. l by a coil spring 49 having one end reacting against pin [6, and the other end thereof received in an opening of the latch lever.

This spring thus tends to holds latch lever 46 in latching position.

In order to manually actuate the circuit breaker contacts, and to reset the mechanism following an automatic circuit interrupting operation in the manner disclosed above, an actuating handle is provided for actuating levers 55, with this handle being of an insulating material, preferably a molded insulating material, and comprising a generally arcuate shaped base portion 80 adapted to lie closely adjacent the arcuate inner surface 62 of the top wall of the casing. The handle structure further includes a handle portion 85 adapted to project through an opening 81 in the casing cover, for manual manipulation at the exterior of the casing. The underside of base portion 66 of the handle structure is provided with a groove for receiving connecting rivet 62 of the actuating levers, and each side of base portion 89 is provided with a recess 84 of substantially the same shape and form as the outer ends of actuating levers 56, to closely frictionally receive the outer ends of these levers. The handle structure is prevented from becoming disengaged from actuating levers 55, by engagement of the base portion 59 thereof with the inner surface of the top wall of the casing. Moreover, base portion 89 of the handle structure acts to substantially close opening 87 in the casing at all positions of the handle. Base portion 89 of the handle structure is provided at one end with spaced depending integral flanges 86 (only one of which is shown), for the purpose of supporting between the outer ends thereof a reset pin 88 suitably mounted in apertures provided in flanges 85.

Now assuming that an automatic circuit interrupting operation has occurred by reason of defiection of bimetal strip 66 to release carrier 49 which has rotated in a clockwise direction about pivot 54 to a position wherein portion 65 thereof engages a stop pin I2, connected between supporting plates Ill, by then moving handle portion 85 to the left, which pivots actuating levers 56 in a counterclockwise direction, engagement of reset pin 68 on the handle structure with projection 89 on carrier d6, will cause movement of the carrier with the handle structure and actuating levers back to the position where the nose 42 thereof may re-engage beneath latch pin 44. This resets carrier 46 to the position shown in Fig. l, and the circuit breaker may then be closed by moving handle portion 85 back to the position shown in Fig. 1. Obviously, actuating levers 56 are moved whenever handle portion 85 is manually moved, so that the breaker contacts may be manually opened and closed by operation of handle portion 85 to cause appropriate movement of actuating levers 56 to operate the breaker contacts in the manner previously described.

In order to prevent accidental release of carrier bar it when the breaker is subjected to mechanical jarring or shock, an inertia latch wheel 98 is provided mounted on one supporting plate II} at one side of latch lever 42, as by a pivot rivet 9 I. The wheel is provided with a pair of pins 92 and 94 projecting from one side thereof toward latch lever 46, and a light coil spring 96 is provided on pin I8 having the ends thereof reacting against pin I6 and pin 94 on the wheel, to normally bias the wheel clockwise and hold the wheel at the position shown in Fig. 1, wherein one pin 92 is in engagement with the adjacent edge of latch lever 46.

When the structure described above is subjected to mechanical shock or jar which would tend to rotate latch lever 46 in a counterclockwise direction to release carrier bar 40, such movement of the latch lever will be imparted to pin 92 of the inertia latch wheel and cause a counterclockwise rotation of this wheel a short distance, until pin 94 thereof engages the latch lever with an impact in the opposite direction, that is, in a direction to maintain the latch pin 44 engaged with carrier bar 40. It is apparent that the more severe such shock may be the greater the impact of pin 94 on the latch lever to prevent release thereof. Latch lever 46 is provided with a ledge 95 adapted to be engaged by pin 92, so that in the event mere impact of pin 92 on the latch lever is inadequate to prevent release of latch lever 46, it is apparent that such movement of the latch lever in a counterclockwise direction as viewed in Fig. l, is positively prevented when pin 92 engages ledge 95, as shown in dotted lines in Fig. 1, because pin 92 blocks or latches the latch lever against release movement. Rebound of the Wheel will occur aided by coil spring 66, as soon as the tendency of the shock to cause release of latch lever 46 subsides, and pin 92 will then impinge upon the latch lever in a direction to maintain latch pin 44 engaged with carrier bar 46. Inertia latch wheel may rebound several times after the impacts of pins 92 and 94, to deliver a series of impacts on the latch lever in a direction to maintain it in engagement with carrier bar 40.

An are confining and extinguishing structure is preferably provided about the space between contacts 24 and 26 when they separate, and this may consist of arc confining plates 98 at each side of the contacts, preferably of an insulating material such for example as fiber or the like. These side plates 98 are connected by spaced transversely extending arc-extinguishing plates I66 having narrow slots IDI at their inner ends for receiving contact bar 22 in its movement. Transverse plates I69 may be of any desired material, preferably iron, and are secured between side plates 98 in any desired manner. An arc barrier plate [62 is also provided across the inner end of the arc confining structure to protect the breaker mechanism, and this plate is provided with a narrow slot I04 substantially in alignment with slots IOI in the reverse plate to receive contact bar 22 in its movement. In operation, the are formed upon operation of contacts 24 and 26 is restricted between side plates 98 and barrier plate I62, and is cooled and confined by transverse plates I06 to provide an efficient arcextinguishing action.

The circuit breaker casing illustrated may also be provided with threaded inserts I96 in the top wall thereof, for mounting purposes or the like.

In Fig. 4 there is illustrated a slightly modified means for supporting contact arm 22, and since all the other parts are identical with those disclosed in Figs. 1 to 3, like reference numerals will be used to designate such like parts. In this embodiment of the invention, a coil compression spring I 68 is adapted to be seated in a recess I It in the bottom wall of the breaker casing, and to engage the underside of contact bar 22 at its other end. Spring IDS is maintained in a position relative to contact bar 22 where, in the closed circuit position, its reaction points are aligned with the pivot axis of pin I6, so that it has no tendency to rotate contact arm 22 about this pivot. An integral projection I I2 provided on contact bar 22 is adapted to be received in the spring to maintain the latter in proper position.

In the operation of the breaker, coil spring I08 acts somewhat differently from leaf spring 34 previously disclosed, because the end coils of spring I68 are positioned in parallel planes, and are adapted to engage parallel surfaces provided at the bottom of recesses H0, and on the lower edge of contact arm 22. This means that when contact bar 22 is pivotally moved to open circuit position, the upper end of spring I08 will be moved to the right, as viewed in Fig. 4, and consequently the tendency of this spring will be to move contact 24 towards open circuit position, thus aiding in opening of the contacts.

In Fig. 5 a spring I 14 is illustrated engaged between the bottom of recess H and a projection l 18 on contact bar 22. In the closed circuit position of the breaker, spring H4 is held at an inclined position as shown in Fig. 5, so that the reaction points of the spring form, in effect, a spring toggle. In the closed circuit position, spring H4 determines the contact pressure of contact 24 on contact 25 in the same way as springs 34 and I08. When contact bar 22 is moved to open circuit position, it will be observed that projection H8 will move the upper end of spring H4 past the center lines of pivot H6 and the point of engagement of spring H4 with the bottom wall of recess I I0, so that continued movement of the contact bar will be assisted by spring H6 because it will then act on the opposite side of pivot I it. At the open circuit position, spring i Hi will act to bias contact bar 22 away from contact 26, to thereby oppose and prevent rebound of the contact bar during a circuit opening operation, and thus avoid the possibility of the arc restriking.

In Figs. 6 and 7 there are illustrated structures very similar to that disclosed in Figs. 1 to 3, except that the slot in the contact bar for receiving pivot pin 15 is disposed at an acute angle to the longitudinal axis of the bar, rather than at substantially 99 as in Figs. 1 to 3. In Fig. 6, where slot I22 is inclined rearwardly, it will be observed that in opening the circuit, spring 34 will cause movement of the inner end of contact bar 22 as before until the bottom of slot 122 engages pin 16. This will obviously cause a longitudinal shifting of contact bar 22 while contacts 2 and 2-5 are engaged, to thereby provide wiping action of these contacts, which is highly desirable in order to maintain clean contact surfaces. Obviously, this wiping action will also occur when the contacts are reclosed. The slot I24. (Fig. 7) is inclined in the opposite direction, and it will be observed that in opening the circuit, the longitudinal shifting of contact bar 22 occurs in a forward direction, to the right as viewed in Fig. 7, and that this movement shifts the lower end of toggle lever 52 to the right, that is, assisting in collapsing the toggle. This results in a speeding up of the tripping time of the breaker since by adjusting the angle of inclination of slot 12 the longitudinal movement of the contact bar reduces the overcenter distance of the toggle any amount down to zero, and thus advance the time at which the contacts will break.

All forms of the invention disclosed embody some means providing a spring mounting for a contact arm at a point spaced from the point of pivotal connection of actuating means for the contact arm and from the contact portion proper, to provide a constant contact pressure irrespective of variation in the size of parts and wear of the contacts, and to also provide a more efficient circuit breaker operating mechanism, In certain 8 forms of this invention, the spring mounting may also assist in moving the contact arm in one direction or another or assist in holding it at an open circuit position, or may embody means for effecting a Wiping action of the contacts during opening and closing of the circuit.

Having described preferred embodiments of the invention as required by the patent statutes, it is desired that it be understood that this invention is not to be limited to these particular embodiments thereof, because it will be obvious, particularly to persons skilled in the art, that many modifications and changes may be made therein without departing from the broad spirit and scope of this invention. Therefore, it is desired that the invention be interpreted as broadly as is possible in the manner defined by the following claims.

We claim as our invention:

1. In a circuit interrupter, a stationary contact, a movable contact arm having a contact portion adjacent one end thereof for engaging said stationary contact, a fixed pivot mounting the other end of said contact arm, actuating means pivotally connected to said contact arm at a point spaced from said contact portion for actuating said contact arm to move said contact portion into and out of engagement wit-h said stationary contact, said contact arm having a slot therein ex endin at an angle to the contacting surfaces through which said pivot extends, and resilient means applying a force on said contact arm at a point adjacent to said pivot and in a direct-ion substantially radially thereof but applying no force to said contact arm tendg to rotate said contact arm about said pivot in opening direction at least in the closed circuit position of said contact arm, whereby said resilient means biases said contact arm about the point of connection with said actuating means to apply contact pressure between said contact portion and said stationary contact.

2. In a circuit interrupter, a contact member which is mounted for movement of a contact portion thereon into and out of engagement with a fixed contact, actuating means for said contact member pivotally connected thereto, pivot means for said contact member, said contact member being slidable relative to said pivot means in a direction at an angle to the plane of the contacting surfaces of said fixed contact and contact portion, resilient means disposed to exert a force on said contact member substantially radially of said pivot means biasing said contact member for sliding movement in a direction to urge said contacting surfaces into engagement at least in the closed circuit position of said interrupter, and said contact portion, said pivot means and the point of connection of said actuating means being in spaced relation alone said contact member, whereby in the closed circuit position said contact member constitutes a lever biased about said point of connection by said resilient means to provide a predetermined contact pressure of said contacting surfaces, there being no component of the force exerted by said resilient means in a direction to rotate said contact member about said pivot means to open circuit position at least when said contact member is at or adjacent closed circuit position.

3. In a circuit interrupter, a contact member which is mounted for movement of a contact portion thereon into and out of engagement with a fixed contact, actuating means for said contact member pivotally connected thereto, pivot means for said contact member, said contact member being slidable relative to said p vot means in a direction substantially at right angles to the plane of the contacting surfaces of said fixed contact and contact portion, resilient means exerting a force on said contact member substantially radially of said pivot means biasing said contact member for sliding movement in a direction to urge said contacting surfaces into engagement but applying no pressure to said pivot means at least in the closed circuit position of said interrupter, and said contact portion, said pivot means and the point of connection of said actuating means being in spaced relation along said contact member, whereby in the closed circuit position said contact member constitutes a lever biased about said point of connection by said resilient means to provide a predetermined contact pressure of said contacting surfaces.

4. In a circuit interrupter, a contact member which is mounted for movement of a contact portion thereon into and out of engagement with a fixed contact, pivot means for said contact member, actuating means for said contact memher, said contact member being slidable relative to said pivot in a direction at an angle to the plane of the contacting surfaces of said fixed contact and contact portion, resilient means normally applying a force substantially radially of said pivot means biasing said contact member for sliding movement in a direction to urge said contacting surfaces into engagement but without applying a force to said pivot means at least in the closed circuit position of said interrupter, said resilient means comprising a spring movable overcenter relative to said pivot means by opening and closing movement of said contact member to assist in moving said contact memher to open and closed positions, and said contact portion, pivot means and the point of connection of said actuating means being in spaced relation along said contact member, whereby in the closed circuit position said contact member constitutes a lever biased about said point of connection by said resilient means to provide a predetermined contact pressure of said contactsurfaces.

5. In a circuit interrupter, a contact member which is mounted for movement of a contact portion thereon into and out of engagement with a fixed contact, pivot means for said contact member, toggle actuating means for said contact member pivotally connected thereto, said contact member being slidable relative to said pivot means in a direction at an acute angle to the plane of the contacting surfaces of said fixed contact and contact portion so as to move the end of said actuating toggle connected thereto towards its dead-center position to assist in breaking the tog le in opening the circuit, resilient means applying a force to said contact member substantially radially of said pivot means, biasing said contact member for sliding movement relative to said pivot means in a direction to urge said contacting surfaces into engagement at least in the closed circuit position of said interrupter, and said contact portion, said pivot means and the point of connection of said actuating means being in spaced relation along said contact member, whereby in the closed circuit position said contact member constitutes a lever biased about said point of connection by said resilient means to provide a predetermined contact pressure of said contacting surfaces.

6. In a circuit interrupter, a contact, a contact member having a contact portion adjacent one end thereof, a pivot for said contact member, said contact member being mounted adjacent the other end thereof on said pivot for movement of said contact portion into and out of engagement with said contact, toggle actuating mechanism pivotally connected with an inter" mediate portion of said contact member, operating means including an overcenter spring adapted to actuate said toggle mechanism to an overcenter position where said contact portion is in engagement with said contact and to a collapsed position where said contact portion is separated from said contact, said contact member being slidable relative to said pivot, and means biasing said contact member for sliding movement relative to said pivot in a direction to maintain a predetermined contact pressure of said contact portion on said contact in the closed circuit position, there being no component of the force exerted by said biasing means in a direction to rotate the contact member about said pivot to open circuit position at least when said contact member is at or adjacent closed circuit position.

'7. In a circuit interrupter, a contact, a contact member having a contact portion adjacent one end thereof, pivot means for said contact member, said contact member being mounted adjacent the other end thereof on said pivot means for movement of said contact portion into and out of engagement with said contact, toggle actuating mechanism pivotally connected with an intermediate portion of said contact member, operating means including an over center spring adapted to actuate said toggle mechanism to an overcenter position Where said contact portion is in engagement with said contact and to a collapsed position Where said contact portion is separated from said contact, said contact member being slidable relative to said pivot means, means biasing said contact member for sliding movement in a direction to maintain a predetermined contact pressure of said contact portion on said contact but Without applying any pressure to said pivot means at least in the closed circuit position, and means for guiding movement or" said contact member in a direction substantially at right angles to the longitudinal axis of said contact member.

8. In a circuit interrupter, a contact, a contact member having a contact portion adjacent one end thereof, pivot means for said contact member, said contact member being mounted adjacent the other end thereof on said pivot means for movement of said contact portion into and out of engagement with said contact, toggle actuating mechanism pivotally connected with an intermediate portion of said contact member, operating means including an overcenter spring adapted to actuate said toggle mechanism to an overcenter position where said contact portion is in engagement with said contact and to a collapsed position where said contact portion is separated from said contact, said contact member being bodily movable relatively to said pivot means, biasing means supplying a force to said contact member substantially radially of said pivot means biasing said contact member in a direction to maintain a predetermined contact pressure of said contact portion on said contact in the closed circuit position but without applying any force to said pivot means, said biasing means comprising a second overcenter spring adapted to be moved overcenter when said contact member moves to open the circuit to prevent rebounding of said contact member.

9. In a circuit interrupter, a contact member which is mounted for pivotal movement of acontact portion thereon into and out of engagement with a fixed contact, pivot means for said contact member, actuating means for said contact member pivotally connected thereto, resilient means applying a force to said contact member substantially radially of said pivot means biasing said contact member for sliding movement relative to said pivot means in a direction to urge saidcontact portion into engagement with said contact at least in the closed position of said interrupter, said contact portion, said pivot means, and the point of connection of said actuating means being in spaced relation along said contact member, said actuating means in a circuit closing operation being moved beyond the point in its closing movement where said contact portion engages said contact, said resil'ent means yielding in response to such additional movement of said actuating means to permit movement of said contact member away from said pivot means so that said resilient means then biases said contact member about said point of connection to provide a predetermined contact pressure and to compensate for wear of the parts, there being no component of the force exerted by said resilient means in a direction to rotate the contact member about said pivot means to open circuit position at least when said contact member is at or adjacent closed circuit position.

10. In a circuit interrupter, a contact member which is mounted for movement of a contact portion thereon into and out of engagement with a fixed contact, actuating means for said contact member pivotally connected thereto, the mounting of said contact member comprising a fixed pivot pin, means defining a slot in said contact member extending in a direction at an angle to the plane of the contacting surfaces of said fixed contact and contact portion, resilient means applying a force on said contact member substantially radially of said pivot pin biasing said contact member in a direction to normali; maintain said pin at one extremity of said slot and yet having no tendency to rotate contact member on said pivot pin in a circuit opening direction when said contact member is at or adjacent its closed circuit position, and said contact portion, mounting, and the point of connection of said actuating means being in spaced relation along said contact member, whereby in the closed circuit position said contact member constitutes a lever biased by said resilient means about said point of connection to provide a predetermined contact pressure of said contacting surfaces.

11, In a circuit interrupter, a contact member which is mounted for movement of a contact portion thereon into and out of engagement with a fixed contact, pivot means for said contact member, actuating means for said contact member pivotally connected thereto, said contact member having a slot therein whereby said contact member is slidable relative to said pivot means in a direction at an angle to the plane of the contacting surfaces of said fixed contact and contact portion, resilient means biasing said contact member for sliding movement relative to said pivot means in a direction to urge said contacting surfaces into engagement at least in the closed circuit position of said interrupter, said resilient means applying a force to said contact member in a direction substantially radially of said pivot means so that the bias thereof has no tendency to rotate said contact member about said pivot means, and said contact portion, said pivot means, and the point of connection of said actuating means being in spaced relation along said contact member, whereby in the closed circuit position said contact member constitutes a lever biased about said point of connection by said resilient means but applying no pressure to said pivot means to provide a predetermined contact pressure of said contacting surfaces.

12. In a circuit interrupter, a contact member which is mounted for movement of a contact portion thereon into and out of engagement with a fixed contact, actuating means for said contact member connected thereto, fixed pivot means for said contact member, said contact member having a slot therein extending at an acute angle to the plane of the contacting surfaces through which said fixed pivot extends to permit sliding action of said contact member relative to said pivot means, the angle of said slot being such as to cause a wiping action of said contact portion across said fixed contact upon engagement and disengagement of said contact portion, resilient means applying a force on said contact member at a point adjacent to said fixed pivot substantially radially of said pivot in a direction to urge the contacting surfaces into engagement at least in the closed circuit position of said interrupter, there being no component of the force exerted by said resilient means in a direction to rotate said contact member about said fixed pivot means to open circuit position at least when said contact member is at or adjacent the closed circuit position, and said contact portion, said fixed pivot means and the point of connection of said actuating means being in spaced relation along said contact member, whereby in the closed circuit position said contact member constitutes a lever biased by said resilient means to provide a predetermined contact pressure of said contacting surfaces.

13. In a circuit interrupter, a contact, a contact member having a contact portion adjacent one end thereof, said contact member being mounted adjacent the other end thereof for movement of said contact portion into and out of engagement with said contact, toggle actuating mechanism pivotally connected with an intermediate portion of said contact member, operating means including an overcenter spring adapted to actuate said toggle mechanism to an overcenter position where said contact portion is in engagement with said contact and to a collapsed position where said contact portion is separated from said contact, said mounting for said contact member comprising a fixed pivot member and means defining a slot in said contact member slidably cooperating with said fixed pivot means, means biasing said contact member about said point of connection with said toggle actuating mechanism in a direction and for sliding movement relative to said fixed pivot member to maintain a predetermined contact pressure of said contact portion on said contact in the closed circuit position, there being no component of the force exerted by said biasing means in a direction to rotate the contact member about said pivot means to open circuit position at least when said contact member is at an adjacent closed circuit position, and said slot being disposed in a direction at an acute angle to the 1ongitudinal axis of said contact member such that on opening of said interrupter said contact member is moved longitudinally in a direction to cause said toggle mechanism to move overcenter.

14. In a circuit interrupter, a contact member which is pivotally mounted for movement of a contact portion thereon into and out of engagement with a fixed contact, fixed pivot means for said contact member, actuating means for said contact member pivotally connected thereto, said contact portion, said pivot means and said point of connection of said actuating means being in spaced relation along said contact member, said actuating means in a circuit closing operation being moved beyond the point in its closing movement when said contact portion engages said fixed contact, biasing means exerting a force on said contact member substantially radially of said fixed pivot biasing said contact member about said point of connection with said actuating means to provide a predetermined contact pressure and to compensate for wear of the parts, there being no component of the force exerted by HILLER D. DORFMAN. GERALD J. FREESE.

REFERENCES CITED The following references are of record in the filo of this patent:

UNITED STATES PATENTS Number Name Date 1,970,421 Flurscheim Aug. 14, 1934 2,015,633 Dorfman Sept. 24, 1935 2,318,298 Dorfman et al May 4, 1943 2,331,012 Woods Oct. 5, 1943 2,334,267 Jackson Nov. 16, 1943 2,416,169 Freese Feb. 18, 1947 

